It is known that the production of paper logs, from which are obtained, for example, rolls of toilet paper or rolls of kitchen paper, involves the feeding of a web of paper, formed by one or more superimposed plies, along a predetermined path where several operations are performed before the formation of the logs, including a transverse pre-incision of the paper web to form the pre-cut lines which divide it into separable sheets. The production of paper logs implies the use of cardboard tubes, commonly said “cores” on whose surface a predetermined amount of glue is distributed to enable the bonding of paper web on the cores introduced into the machine that produces logs, commonly said “rewinder”. The glue is distributed on the cores when they pass along a corresponding path comprising an end part that is commonly called “cradle” for its concave conformation. The formation of logs implies, also, the use of winding rollers downstream of the cradle, which make each core to rotate about its longitudinal axis thus causing the winding of the web on the core. The process ends when a predetermined number of sheets is wound on the core, with the gluing of an edge of the last sheet on the underlying one of the roll thus formed (so-called “edge-closing” operation). At this point, the log is discharged from the rewinder.
EP1519886 discloses a rewinding machine performing the operations described above.
A drawback connected with the use of conventional rewinders resides in the fact that the paper web at an initial stage of winding on the core, given the fixed position of the winding rollers, forms a series of narrower windings. Therefore, the finished log features zones that are more compact compared to other zones of the same log, determined by said configuration of the machine, in which zones the winding density in the radial direction is greater, and less compressed areas, in which the winding density is lower. Therefore, the appearance of the finished product is not optimal and there is also a higher consumption of paper when the end of the process is determined by the achievement of a predetermined diameter of the log. In this context, the winding density can be defined as the number of sheets counted along a radial direction of the log divided by the radial length of the zone where the winding density is measured. To overcome the aforementioned drawback, rewinders have been produced in the past having a mobile winding roller that allows a better control of the first layers of paper wound on the core. However, such a solution is still improvable because at a certain point of the mobile winding roller movement, i.e. when the log being formed reaches a given diameter, the latter, with the further movement of the mobile winder roller, interferes with the end part of the cradle and is subject to damages leading to the breaking of the paper web and, therefore, to the machine stop.
A rewinder having elastic means adapted to allow a modification of the shape of the end part of the guide defining the path followed by the cores is disclosed in WO2010/004521.